1. Field of the Invention
The invention relates to a device for positioning and melting electrically conductive materials without a receptacle.
2. Description of Related Art
It is known to contactlessly melt metals or alloys between two vertically separated coils, through which a high-frequency alternating current flows in respectively opposite direction. The coils have a double function: They serve as positioning coils for holding the sample in the melting area, and they generate eddy currents in the sample by magnetic induction, thereby heating the sample. A sample, arranged under zero-gravity conditions and thus not submitted to any timely constant exterior forces, is fixed in the magnetic field of both coils at the point at which the combined magnetic field of both coils is weakest, or forced back to that point by small mechanic shocks. In doing so, however, the metal sample is located in an area where the value of magnetic flux density, and, thus, also the heat generated by the eddy currents, is lowest. The heating efficiency of a coil arrangement in which a high-frequency current flows through the coils in opposite directions and in phase, which thereby generate a magnetic quadrupolefield, is very low, whereas the positioning forces are comparatively high.
In order to obtain not only high positioning forces, but also a strong heating effect, German Patent publication No. .-+.39 973 A1, in addition to the coils generating the positioning field, provides at least one further coil surrounding the melting area, through which a high-frequency current of a higher frequency flows. This further coil serves as a heating coil for a contactless inductive heating of the sample. Since the strength of the magnetic field generated by this coil is greatest in the area of the sample held by the positioning field, the energy of the alternating current flowing in this coil is transformed into melting heat within the sample. However, it is a disadvantage that the two coils generating the positioning field are located very close to the heating coil so that a rather high magnetic field strength prevails in the area between the heating coil and a respective positioning coil. This has the effect that the positioning coils are heated by the heating coils to almost the same degree as the sample itself. This heat has to be cooled down and is lost. On the other hand, the heating coil screens off a large part of the fields of the positioning coils from the sample, thereby significantly reducing their force efficiency, so that a considerable part of the power applied to the positioning coils is also transformed into useless heat.
It is an object of the present invention to provide a device for positioning and melting electrically conductive materials without a receptacle which allows a melting and a positioning of a sample with low heat dissipation and high efficiency.